Method And Apparatus For Multi-Phase DC-DC Converters Using Coupled Inductors In Discontinuous Conduction Mode

ABSTRACT

A multiphase DC-DC converter includes a coupled inductor, N phases of the multiphase DC-DC converter, and a controller, where N is an integer greater than 2. The coupled inductor includes a plurality of inductors. Each inductor is coupled to two neighboring inductors or to rest of the inductors. The N phases of the multiphase DC-DC converter are respectively connected to the plurality of inductors. The controller operates the multiphase DC-DC converter in continuous conduction mode and in discontinuous conduction mode. Body diodes of switches in the N phases do not conduct when the multiphase DC-DC converter operates in discontinuous conduction mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/972,381 filed on May 7, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/283,915 filed on Oct. 3, 2016 (now U.S. Pat. No.9,966,853) which claims the benefit of U.S. Provisional Application No.62/237,318 filed on Oct. 5, 2015. The entire disclosures of theapplications referenced above are incorporated herein by reference.

FIELD

The present disclosure relates generally to switching power supplies andmore particularly to improving light load power efficiency of multiphaseswitching converters using coupled inductors in discontinuous conductionmode.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

A multiphase coupled-inductor DC-DC converter operates in continuousconduction mode (CCM) when the output power demand is high and indiscontinuous conduction mode (DCM) when the output power demand is low.Most DC-DC converters that deliver high current operate in CCM, wherehigh and low side switches of the DC-DC converter switch on and offalternately, and current in a coupled inductor of the DC-DC converterramps up and down continuously. CCM enables the DC-DC converter todeliver high current with high efficiency.

In DCM, the DC-DC converter delivers energy to the load only whenneeded. When energy is needed, a high side switch turns on for certainamount of time. After the high side switch turns off, a low side switchturns on. As inductor current drops to zero, the low side switchturns-off. When energy is not needed, the switches of the DC-DCconverter stop switching and remain off until energy is needed. When theswitches are off, the inductor current remains zero; and an outputfilter capacitor supports the current when both switches are off.Accordingly, in DCM, the switching loss and the AC current related lossscale down with decreasing load current, and the DC-DC convertermaintains high efficiency even at light load.

SUMMARY

A multiphase DC-DC converter comprises a coupled inductor that includesfirst and second inductors coupled together, a first phase includingfirst high side and low side switches connected to the first inductor, asecond phase including second high side and low side switches connectedto the second inductor, and a controller that drives the first andsecond high side switches and the first and second low side switches tooperate the DC-DC converter in discontinuous conduction mode. Throughoutthe present disclosure, first and second phases are used for exampleonly, and the teachings of the present disclosure apply to multi-phaseconverters comprising more than two phases. Similarly, while theexamples described include buck (step-down) converters operating withpositive output current, the teachings of the present disclosure applyequally to buck converters with negative output current or high sidebody diode conduction, as well as to boost converters, buck-boostconverters, and other topologies where coupled inductors are applicable.The controller determines, in response to the first high side switchbeing turned on and the second low side switch being turned off, thatcoupling between the first inductor and the second inductor is strong orweak based on whether a body diode of the second low side switchconducts or does not conduct. Strong or weak coupling can also bedetected based on when a first phase high side switch turns on and asecond phase low side switch is on, and inductor current in a secondphase low side switch has positive polarity or negative polarity. Thecontroller performs the following functions depending on whether thecoupling is strong or weak: If the coupling is strong, if high sideswitch of a first phase is on and low side switch of a second phase isoff, turn on low side switch of the second phase; if low side switch ofthe second phase is on, keep it on. If the coupling is weak, if highside switch of a first phase is on and low side switch of a second phaseis off, do not turn on low side switch of a second phase; If high sideswitch of a first phase is on and low side switch of a second phase ison, keep low side switch of the second phase on. This operation extendsto all cases disclosed below where coupling between phases is an issue.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. A third switch isconnected between the first high side and low switches, where bodydiodes of the third switch and the first low side switch are connectedback-to-back. A fourth switch is connected between the second high sideand low switches, where body diodes of the fourth switch and the secondlow side switch are connected back-to-back. A controller drives thefirst and second high side switches and the first and second low sideswitches to operate the DC-DC converter in discontinuous conductionmode. The controller turns on the fourth switch only in response to thefirst high side switch being turned on, and turns on the third switchonly in response to the second high side switch being turned on, wherebody diodes of first and second low side switches do not conduct.Further, the controller can detect whether coupling between the firstand second phases is strong or weak, and if the coupling is weak, athird switch that is always on can be added in each phase to saveswitching power in weak coupling case.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. A third switch isconnected across bulk and drain terminals of the second low side switch.A fourth switch is connected across bulk and source terminals of thesecond low side switch. A controller drives the first and second highside switches and the first and second low side switches to operate theDC-DC converter in discontinuous conduction mode. The controller turnson the fourth switch in response to the first high side switch beingturned on and a voltage at a junction of the second high side and lowside switches having a first polarity. The controller turns on the thirdswitch in response to the first high side switch being turned on and thevoltage at the junction of the second high side and low side switcheshaving a second polarity that is opposite to the first polarity. A bodydiode of the second low side switch does not conduct. Further, thecontroller can detect whether coupling between the first and secondphases is strong or weak, and if the coupling is weak, a third switchthat is always off and a fourth switch that is always on can be added ineach phase to save switching power in weak coupling case.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together; afirst phase including first high side and low side switches connected tothe first inductor, where the first low side switch includes a firstplurality of switches connected in series; and a second phase includingsecond high side and low side switches connected to the second inductor,where the second low side switch includes a second plurality of switchesconnected in series. A controller drives the first and second high sideswitches and the first and second low side switches to operate the DC-DCconverter in discontinuous conduction mode. Body diodes of first andsecond low side switches do not conduct. Further, the controller candetect whether coupling between the first and second phases is strong orweak, and if the coupling is weak, the controller keeps the secondplurality of switches always on to save switching power in weak couplingcase.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. A third switch isconnected across bulk and source terminals of the second low sideswitch. A fourth switch is connected across bulk terminal of the secondlow side switch and a voltage source. A controller drives the first andsecond high side switches and the first and second low side switches tooperate the DC-DC converter in discontinuous conduction mode. Thecontroller turns off the third switch and turns on the fourth switch inresponse to the first high side switch being turned on. A body diode ofthe second low side switch does not conduct. Further, the controller candetect whether coupling between the first and second phases is strong orweak, and if the coupling is weak, a third switch that is always on anda fourth switch that is always off can be added in each phase to saveswitching power in weak coupling case.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, anda third inductor that is not coupled to the first and second inductors.First and second phases of the DC-DC converter are respectivelyconnected to the first and second inductors. A third phase of the DC-DCconverter is connected to the third inductor. A controller selects thefirst and second phases in response to operating the DC-DC converter incontinuous conduction mode, and selects the third phase in response tooperating the DC-DC converter in discontinuous conduction mode.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes a first inductor and a plurality of inductors,where the first inductor is coupled to each of the plurality ofinductors. A first phase and a plurality of phases of the DC-DCconverter are respectively connected to the first inductor and theplurality of inductors. A controller selects the first phase in responseto operating the DC-DC converter in discontinuous conduction mode, andselects one or more of the first phase and the plurality of phases inresponse to operating the DC-DC converter in continuous conduction mode.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes a plurality of inductors, each inductor beingcoupled to two neighboring inductors or to rest of the inductors. Aplurality of phases of the DC-DC converter is respectively connected tothe plurality of inductors. A controller operates the DC-DC converter incontinuous conduction mode and in discontinuous conduction mode. Bodydiodes of switches in the plurality of phases do not conduct when theDC-DC converter operates in discontinuous conduction mode.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. A controller drivesthe first and second high side switches and the first and second lowside switches to operate the multiphase DC-DC converter. In response tooperating the multiphase DC-DC converter in discontinuous conductionmode and in response to the first high side switch being turned on, thecontroller prevents conduction of a body diode of the second low sideswitch by bypassing current around the second low side switch bodydiode, blocking current from flowing through the second low side switchbody diode, or increasing threshold for conduction of the second lowside switch body diode.

In other features, the controller prevents second low side switch bodydiode conduction, depending on a strength of coupling between the firstinductor and the second inductor. The controller determines, in responseto the first high side switch being turned on and the second low sideswitch being turned off, that coupling between the first inductor andthe second inductor is strong or weak, based on whether the body diodeof the second low side switch will conduct if not prevented fromconducting. The controller prevents second low side switch body diodeconduction in response to the first high side switch being turned onwhen the coupling is strong. The controller does not prevent second lowside switch body diode conduction in response to the first high sideswitch being turned on when the coupling is weak.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is strong or weak based oncurrents through one or more of the first and second inductors of thecoupled inductor; or currents through one or more of the first andsecond high side and/or low side switches; or voltages at one or more ofa first node at which the first inductor is connected to the first highside and low side switches and a second node at which the secondinductor is connected to the second high side and low side switches.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is weak, based on the bodydiode of the second low side switch not conducting when the first highside switch is turned on and when the second low side switch is turnedoff. The controller determines that the coupling between the firstconductor and the second conductor is strong, based on the body diode ofthe second low side switch conducting when the first high side switch isturned on and when the second low side switch is turned off.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is weak, based on a voltageat a node at which the second inductor is connected to the second highside and low side switches not being clamped by the body diode of thesecond low side switch when the first high side switch is turned on andwhen the second low side switch is turned off. The controller determinesthat the coupling between the first conductor and the second conductoris strong based on the voltage at the node being clamped by the bodydiode of the second low side switch when the first high side switch isturned on and when the second low side switch is turned off.

In other features, the controller turns on the second low side switch inresponse to the first high side switch being turned on when the couplingis strong, to prevent the body diode of the second low side switch fromconducting. The controller does not turn on the second low side switchin response to the first high side switch being turned on when thecoupling is weak, to prevent negative current flow through the secondlow side switch.

In still other features, the multiphase DC-DC converter furthercomprises a fifth switch connected between the first high side and lowside switches. The body diodes of the fifth switch and the first lowside switch are connected back-to-back. The multiphase DC-DC converterfurther comprises a sixth switch connected between the second high sideand low side switches. The body diodes of the sixth switch and thesecond low side switch are connected back-to-back. The controllerdecreases a tendency for conduction of body diodes of the first andsecond low side switches by turning off the sixth switch in response tothe first high side switch being turned on and by turning off the fifthswitch in response to the second high side switch being turned on,whereby the body diodes of the first and second low side switches do notconduct.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns on the fifth and sixth switches.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the fifth or sixth switches. The body diodes of the first andsecond low side switches do not conduct irrespective of strength ofcoupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on and whereinductor currents of the first and second phases do not overlap, thefirst control signal and a third control signal that drives the firsthigh side switch are of opposite polarities.

In still other features, the multiphase DC-DC converter furthercomprises a fifth switch connected across bulk and drain terminals ofthe second low side switch and a sixth switch connected across bulk andsource terminals of the second low side switch. The controller decreasesa tendency for conduction of the body diodes of the second low sideswitch by turning on the sixth switch in response to the first high sideswitch being turned on and a voltage at a junction of the second highside and low side switches having a first polarity, and by turning onthe fifth switch in response to the first high side switch being turnedon and the voltage at the junction of the second high side and low sideswitches having a second polarity that is opposite to the firstpolarity. The body diodes of the second low side switch do not conduct.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the first or second low side switch. The body diodes of thefirst and second low side switches do not conduct irrespective ofstrength of coupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns off the fifth switch and turns on the sixth switch.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on, the fifth andsixth switches are turned on or off based on the voltage at the junctionof the second high side and low side switches.

In still other features, the first low side switch includes a firstplurality of switches connected in series, and the second low sideswitch includes a second plurality of switches connected in series. Thecontroller decreases a tendency for conduction of body diodes of thefirst and second low side switches by controlling the first and secondplurality of switches. The body diodes of the first and second low sideswitches do not conduct.

In other features, the first and second plurality of switches decrease atendency for conduction of the body diodes of the first and second lowside switches and prevent conduction of the body diodes of first andsecond low side switches.

In other features, if an integer N greater than 1 denotes a number ofswitches in each of the first and second plurality of switches, voltagesat nodes at which the first and second high side switches are connectedto the first and second low side switches are negative by N times aforward voltage drop of a body diode of a switch in the first and secondplurality of switches to prevent conduction of the body diodes of firstand second low side switches.

In other features, each of the first and second phases includes aplurality of level shifters that convert a control signal from thecontroller from a first supply rail to a second supply rail comprising avoltage lower than a switching node voltage and that output a pluralityof control signals to drive the first and second plurality of switches.The body diodes of the first and second low side switches do not conductirrespective of strength of coupling between the first inductor and thesecond inductor.

In still other features, the multiphase DC-DC converter furthercomprises a fifth switch connected across bulk and source terminals ofthe second low side switch and a sixth switch connected across bulkterminal of the second low side switch and a voltage source. Thecontroller decreases a tendency for conduction of the body diode of thesecond low side switch by turning off the fifth switch and turning onthe sixth switch in response to the first high side switch being turnedon. The body diode of the second low side switch does not conduct.

In other features, the voltage source supplies a voltage of the samepolarity as the type of a dopant used for the switches.

In other features, in each of the first and second phases, in responseto the switches using N type dopant, the voltage source supplies anegative voltage that is more negative than a lowest voltage at aswitching node to prevent body diodes of the first and second low sideswitches from conducting.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the first or second low side switch. The body diodes of thefirst and second low side switches do not conduct irrespective ofstrength of coupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns on the fifth switch and turns off the sixth switch.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on, thecontroller turns off the fifth switch and turns on the sixth switch.

In still other features, an inductance matrix of the coupled inductorensures that a coupling voltage across the body diode is less than aforward voltage drop of the body diode.

In still other features, the controller blocks current from flowingthrough the body diode in the event that a voltage across the second lowside switch is greater than a forward voltage drop of the body diode.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. A controller drivesthe first and second high side switches and the first and second lowside switches to operate the multiphase DC-DC converter in discontinuousconduction mode. The controller determines, in response to the firsthigh side switch being turned on and the second low side switch beingturned off, that coupling between the first inductor and the secondinductor is strong or weak based on whether a body diode of the secondlow side switch will conduct if not prevented from conducting. Thecontroller prevents second low side switch body diode conduction inresponse to the first high side switch being turned on when the couplingis strong. The controller does not prevent second low side switch bodydiode conduction in response to the first high side switch being turnedon when the coupling is weak.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is strong or weak based oncurrents through one or more of the first and second inductors of thecoupled inductor, or currents through one or more of the first andsecond high side and/or low side switches, or based on voltages at oneor more of a first node at which the first inductor is connected to thefirst high side and low side switches and a second node at which thesecond inductor is connected to the second high side and low sideswitches.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is weak based on the bodydiode of the second low side switch not conducting when the first highside switch is turned on and when the second low side switch is turnedoff. The controller determines that the coupling between the firstinductor and the second inductor is strong based on the body diode ofthe second low side switch conducting when the first high side switch isturned on and when the second low side switch is turned off.

In other features, the controller determines that the coupling betweenthe first inductor and the second inductor is weak based on a voltage ata node at which the second inductor is connected to the second high sideand low side switches not being clamped by the body diode of the secondlow side switch when the first high side switch is turned on and whenthe second low side switch is turned off. The controller determines thatthat the coupling between the first inductor and the second inductor isstrong based on the voltage at the node being clamped by the body diodeof the second low side switch when the first high side switch is turnedon and when the second low side switch is turned off.

In other features, the controller turns on the second low side switch inresponse to the first high side switch being turned on when the couplingis strong to prevent the body diode of the second low side switch fromconducting, and does not turn on the second low side switch in responseto the first high side switch being turned on when the coupling is weakto prevent negative current flow through the body diode of the secondlow side switch.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. The multiphase DC-DCconverter further comprises a third switch connected between the firsthigh side and low switches, where body diodes of the third switch andthe first low side switch are connected back-to-back; and a fourthswitch connected between the second high side and low switches, wherebody diodes of the fourth switch and the second low side switch areconnected back-to-back. A controller drives the first and second highside switches and the first and second low side switches to operate themultiphase DC-DC converter. In response to the controller operating themultiphase DC-DC converter in discontinuous conduction mode, thecontroller turns on the fourth switch only in response to the first highside switch being turned on and turns on the third switch only inresponse to the second high side switch being turned on. The body diodesof the first and second low side switches do not conduct.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the third or fourth switches. The body diodes of the first andsecond low side switches do not conduct irrespective of strength ofcoupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns on the third and fourth switches.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on and whereinductor currents of the first and second phases do not overlap, thefirst control signal and a third control signal that drives the firsthigh side switch are of opposite polarities.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. The multiphase DC-DCconverter further comprises a third switch connected across bulk anddrain terminals of the second low side switch and a fourth switchconnected across bulk and source terminals of the second low sideswitch. A controller drives the first and second high side switches andthe first and second low side switches to operate the multiphase DC-DCconverter. In response to the controller operating the multiphase DC-DCconverter in discontinuous conduction mode, the controller turns on thefourth switch in response to the first high side switch being turned onand a voltage at a junction of the second high side and low sideswitches having a first polarity, and turns on the third switch inresponse to the first high side switch being turned on and the voltageat the junction of the second high side and low side switches having asecond polarity that is opposite to the first polarity. A body diode ofthe second low side switch does not conduct.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the first or second low side switch. The body diodes of thefirst and second low side switches do not conduct irrespective ofstrength of coupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns off the third switch and turns on the fourth switch.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on, the third andfourth switches are turned on or off based on the voltage at thejunction of the second high side and low side switches.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together; afirst phase including first high side and low side switches connected tothe first inductor, where the first low side switch includes a firstplurality of switches connected in series; and a second phase includingsecond high side and low side switches connected to the second inductor,where the second low side switch includes a second plurality of switchesconnected in series. A controller drives the first and second high sideswitches and the first and second low side switches to operate themultiphase DC-DC converter in discontinuous conduction mode. The bodydiodes of the first and second low side switches do not conduct.

In other features, the first and second plurality of switches decrease atendency for conduction of the body diodes of the first and second lowside switches and prevent conduction of the body diodes of first andsecond low side switches.

In other features, if an integer N greater than 1 denotes a number ofswitches in each of the first and second plurality of switches, voltagesat nodes at which the first and second high side switches are connectedto the first and second low side switches are negative by N times aforward voltage drop of a body diode of a switch in the first and secondplurality of switches to prevent conduction of the body diodes of firstand second low side switches.

In other features, each of the first and second phases includes aplurality of level shifters that convert a control signal from thecontroller from a first supply rail to a second supply rail comprising avoltage lower than a switching node voltage and that output a pluralityof control signals to drive the first and second plurality of switches.The body diodes of the first and second low side switches do not conductirrespective of strength of coupling between the first inductor and thesecond inductor.

In another feature, a multiphase DC-DC converter comprises a coupledinductor that includes first and second inductors coupled together, afirst phase including first high side and low side switches connected tothe first inductor, and a second phase including second high side andlow side switches connected to the second inductor. The multiphase DC-DCconverter further comprises a third switch connected across bulk andsource terminals of the second low side switch and a fourth switchconnected across bulk terminal of the second low side switch and avoltage source. A controller drives the first and second high sideswitches and the first and second low side switches to operate themultiphase DC-DC converter. In response to the controller operating themultiphase DC-DC converter in discontinuous conduction mode, thecontroller drives the first and second high side switches and the firstand second low side switches to operate the multiphase DC-DC converterin discontinuous conduction mode, and turns off the third switch andturns on the fourth switch in response to the first high side switchbeing turned on. A body diode of the second low side switch does notconduct.

In other features, the voltage source supplies a voltage of the samepolarity as the type of a dopant used for the switches.

In other features, in each of the first and second phases, in responseto the switches using N type dopant, the voltage source supplies anegative voltage that is more negative than a lowest voltage at aswitching node to prevent body diodes of the first and second low sideswitches from conducting.

In other features, each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the first or second low side switch. The body diodes of thefirst and second low side switches do not conduct irrespective ofstrength of coupling between the first inductor and the second inductor.

In other features, in response to the controller operating themultiphase DC-DC converter in continuous conduction mode, the controllerturns on the third switch and turns off the fourth switch.

In other features, in response to the controller operating themultiphase DC-DC converter in skip mode where the second low side switchis turned on when the first high side switch is turned on, thecontroller turns off the third switch and turns on the fourth switch.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic of a two-phase coupled inductor DC-DC converter;

FIG. 2 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 1 in discontinuous conduction mode(DCM);

FIGS. 3-5 depict show different ways of operating the two-phase coupledinductor DC-DC converter of FIG. 1 at light load in DCM;

FIG. 6 is a schematic of a two-phase coupled inductor DC-DC converterthat detects coupling strength of the coupled inductor and that bypassesa body diode of a low side switch of when the coupling is weak in DCM;

FIG. 7 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 6 in DCM;

FIG. 8 is a schematic of a two-phase coupled inductor DC-DC converterthat blocks body diode current flow when coupling strength of thecoupled inductor is weak in DCM;

FIG. 9 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 8 in DCM;

FIG. 10 is a schematic of a two-phase coupled inductor DC-DC converterthat prevents body diode conduction in DCM using a low side switchcomprising back-to-back series connected switches;

FIG. 11 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 10 in DCM;

FIG. 12 is a schematic of a two-phase coupled inductor DC-DC converterthat prevents body diode conduction in DCM by switching bulk connectionsof the low side switches;

FIG. 13 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 12 in DCM;

FIG. 14 is a schematic of a two-phase coupled inductor DC-DC converterthat prevents body diode conduction in DCM using a low side switchcomprising a plurality of series-connected switches;

FIG. 15 is a schematic of a two-phase coupled inductor DC-DC converterthat prevents body diode conduction in DCM by biasing the bulk of thelow side switches to a more negative voltage;

FIG. 16 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 15 in DCM;

FIG. 17 is a schematic of a two-phase coupled inductor DC-DC converterthat prevents body diode conduction in DCM using modified coupledinductor topologies and/or connections;

FIG. 18 is a timing diagram showing operation of the two-phase coupledinductor DC-DC converter of FIG. 17 in DCM;

FIGS. 19 and 20 depict examples of modified coupled inductor topologiesand/or connections that can be used in the two-phase coupled inductorDC-DC converter of FIG. 17;

FIG. 21 shows a flowchart of a method for preventing conduction of abody diode of a low side switch of a coupled-inductor DC-DC converteroperating at light load in DCM by detecting strong or weak coupling;

FIG. 22 shows a flowchart of a method for preventing conduction of abody diode of a low side switch of a coupled-inductor DC-DC converteroperating at light load in DCM by using a low side switch comprisingback-to-back series connected switches;

FIG. 23 shows a flowchart of a method for preventing conduction of abody diode of a low side switch of a coupled-inductor DC-DC converteroperating at light load in DCM by switching bulk connections of the lowside switch;

FIG. 24 shows a flowchart of a method for preventing conduction of abody diode of a low side switch of a coupled-inductor DC-DC converteroperating at light load in DCM by using a low side switch comprising aplurality of series-connected switches; and

FIG. 25 shows a flowchart of a method for preventing conduction of abody diode of a low side switch of a coupled-inductor DC-DC converteroperating at light load in DCM by biasing bulk of the low side switchusing a voltage source.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

FIG. 1 shows an example of a two-phase coupled-inductor DC-DC converter100. Each phase of the converter 100 includes a high side (HS) switchand a low side (LS) switch. The two phases are connected to a coupledinductor, which includes two inductors L1 and L2 that are coupledtogether. The coupled inductor has a magnetizing inductance L_(m). Eachof the inductors L1 and L2 has a corresponding leakage inductance L_(k).The coupled inductor is connected to a load. A filter capacitor isconnected across the load. A controller 102 generates pulse-widthmodulated (PWM) pulses that drive the HS and LS switches of the twophases as shown in FIG. 2. The controller 102 operates the converter 100in CCM or DCM based on the power demand as follows.

In CCM, the controller 102 monitors an output voltage Vout at thecapacitor. The controller 102 generates the PWM pulses to alternatelyturn on the first or second high side switches HS1 or HS2, which buildscurrent through the associated winding L1 or L2 of the coupled inductor.As the current builds, magnetic coupling produces current through theun-driven winding L2 or L1 of the coupled inductor, and the associatedlow side switch LS2 or LS1 is turned on so that current through bothwindings L1 and L2 of the coupled inductor can charge the capacitor.

At the end of this part of the cycle, the high side switch HS1 or HS2 isturned off and the associated low side switch LS1 or LS2 is turned on sothat both low side switches LS1 and LS2 are on. Current through thewindings L1 and L2 of the coupled inductor decreases and may reverse. Asthe current decreases, the controller 102 may turn on a different one ofthe high side switches HS2 or HS1 while turning off the correspondinglow side switch LS2 or LS1. This builds current through the associatedwinding L2 or L1 of the coupled inductor. As the current builds,magnetic coupling produces current through the now un-driven winding L1or L2 of the coupled inductor, and the associated low side switch LS1 orLS2 is turned on so that current through both windings L12 and L2 of thecoupled inductor can charge the capacitor. This cycle repeats as theconverter 100 operates in CCM.

Each low side switch LS1 and LS2 has a body diode. For high efficiencyat low operating voltages, to avoid power dissipation in the bodydiodes, the low side switches LS1 and LS2 are turned on. The outputvoltage Vout is controlled by varying a duration for which each highside switch HS1 and HS2 is held on to maintain a suitable outputvoltage. The output voltage Vout can be controlled using voltage modecontrol, current mode control, or any other control method.

In DCM operation, the controller 102 monitors the output voltage Vout.When Vout drops below a threshold Vth, an energy delivery pulse begins.During a first energy delivery pulse, the high side switch HS1 is turnedon, and the low-side switch LS2 for an inductively coupled oppositephase is turned on. As current builds in the winding L1 associated withthe high side switch HS1, a similar current is induced in the winding L2associated with the low side switch LS2. After the high-side switch HS1has been on for a pulse width Tpw, the high side switch HS1 is turnedoff, and the corresponding low side switch LS1 is turned on. Aftercurrent through the windings L1 and L2 of the coupled inductor decays tozero, the low side switches LS1 and LS2 are turned off. The cyclerepeats as the controller 102 monitors Vout.

Throughout the present disclosure, in DCM, the terms strong coupling andweak coupling between the inductors of the coupled inductor are used tomean the following. In DCM, when a high side switch of a first phase ison and a low side switch of a second phase is off, the coupling betweenthe inductors of the coupled inductor is strong if the body diode of thelow side switch conducts and is weak if the body diode of the low sideswitch does not conduct.

FIGS. 3-5 show different ways of operating the converter 100 at lightload in DCM. In FIG. 3, in DCM, the body diode of the low side switchLS2 is simply allowed to conduct. When the high side switch HS1 isturned on, the low side switch LS2 is kept off. In strong coupling case(high L_(m)/L_(k) ratio and low converter duty cycle), the voltage atthe switching node LX2 of phase 2 can be less than the forward voltagedrop of the body diode of the low side switch LS2. Consequently, thebody diode of the low side switch LS2 will conduct and generate extrabody diode conduction loss, which can drop converter efficiency by5-20%.

In FIG. 4, in DCM, when the high side switch HS1 is turned on, the lowside switch LS2 is also turned on; and when the high side switch HS2 isturned on, the low side switch LS1 is also turned on. When the high sideswitch HS1 is turned on, and the low side switch LS2 is also turned on,for strong coupling, inductor current IL2 flowing through phase 2 willhave positive slope (direction as indicated by arrow); and for weakcoupling, inductor current IL2 flowing through phase 2 will havenegative slope (direction opposite of that indicated by arrow), whichdecreases converter efficiency. Similar result is obtained when the highside switch HS2 is turned on, and the low side switch LS1 is also turnedon.

In FIG. 5, in DCM, the phases are switched on and off in parallel. Foreach phase, the equivalent inductance is equal to the leakageinductance, which is low. If the on-time of the switches is kept thesame as in CCM, the peak inductor current in DCM will be very high dueto the low leakage inductance, which increases ripple and decreasesefficiency. If the on-time is reduced in DCM, the switching frequencywill be high since small amount of energy will be delivered in eachcycle.

The present disclosure eliminates the unwanted conduction of the bodydiode of the low side switch or the unwanted conduction of the low sideswitch in coupled phases of DC-DC converters operating in DCM toincrease efficiency. Specifically, in one implementation, by detectingstrong or weak coupling, the present disclosure eliminates body diodeconduction in strong coupling by turning on the low side switch andeliminates negative body diode current in weak coupling by turning offthe low side switch as explained below in detail.

The present disclosure proposes three classes of solutions to preventconduction of the body diode of the low side switch: bypassing currentaround the body diode of the low side switch to reduce conduction losseswhen needed; blocking current from flowing through the body diode of thelow side switch; and limiting voltage across the body diode of the lowside switch to less than the forward voltage drop of the body diode.That is, for multiphase switching DC-DC converters with coupledinductors operating at light load (i.e., in DCM), when a high sideswitch of a first phase is turned on, the body diode of a low sideswitch of a second phase is adaptively bypassed if needed, blocked byspecific design, or prevented from conducting by reducing forwardvoltage across the body diode.

While the present disclosure uses a two-phase DC-DC converter forexample only, the teachings of the present disclosure can be extended toDC-DC converters comprising more than two phases. Further, throughoutthe present disclosure, while the operations are described in terms ofhow phase 2 is controlled when phase 1 is turned on for example only,phase 1 can be similarly controlled when phase 2 is turned on. Also,while NMOS switches are shown for example only, PMOS (or any othersuitable switches) can be used instead, where polarities and directionsof voltages and currents, and logic levels of signals shown anddescribed below may be reversed accordingly. Further, while the proposedsolutions focus on DCM and light load operations, the controllers andconverters disclosed herein are designed to and can in fact operate inCCM and DCM over light, medium, and heavy load conditions.

FIG. 6 shows a controller 104 that controls the converter 100. Thecontroller 104 detects whether coupling between the inductors of thecoupled inductor is strong or weak, and bypasses a body diode of a lowside switch of depending on the coupling strength of the coupledinductor. The controller 104 can detect the coupling strength of thecoupled inductor in many ways. For example, the controller 104 candetect the coupling strength of the coupled inductor by sensing currentsIL1 and IL2 through the inductors L1 and/or L2 of the coupled inductor;by sensing voltages at the switching nodes LX1 and/or LX2 of the phasesof the converter 100; and so on.

For example, the controller 104 determines that the coupling is weak, ifthe body diode of the low side switch LS2 does not conduct when the lowside switch LS2 is off and the high side switch HS1 is on.Alternatively, the controller 104 determines that the coupling is weak,if the voltage at the switching node LX2 of phase 2 is positive (forNMOS switches, or negative for PMOS switches) when the low side switchLS2 is off and the high side switch HS1 is on.

Conversely, the controller 104 determines that the coupling is strong,if the body diode of the low side switch LS2 conducts when the low sideswitch LS2 is off and the high side switch HS1 is on; or if the voltageat the switching node LX2 of phase 2 is negative (for NMOS switches, orpositive for PMOS switches) when the low side switch LS2 is off and thehigh side switch HS1 is on. The threshold between strong and weakcoupling may not be chosen exactly at the boundary of where the low sidebody diode would conduct if not prevented.

In DCM, when the high side switch HS1 is on, the controller 104 controlsthe low side switch LS2 based on the coupling strength of the coupledinductor as follows: the controller 104 turns on the low side switch LS2if the coupling is strong to prevent body diode conduction, and thecontroller 104 does not turn on the low side switch LS2 if the couplingis weak to prevent negative current flow through the body diode. Thus,by turning the low side switch LS2 on and off when the coupling strengthof the coupled inductor is strong and weak eliminates any current flowthrough the body diode of the low side switch LS2 in DCM at light load.FIG. 7 shows that while the controller 102 of FIG. 1 turns on the lowside switch LS2 when the coupling is weak, the controller 104 of FIG. 6does not turn on the low side switch LS2 when the coupling is weak andbypasses the body diode of the low side switch LS2 when the coupling isweak.

In FIG. 1, for 2 coupled phases, when the high side switch HS 1 of phase1 is turned on, phase 2 stays in high impedance (both HS2 and LS2 areoff). If coupling between two phases is strong, the switching nodevoltage LX2 of the coupling phase (phase 2) will be negative enough toforward bias the body diode of the low side switch LS2 of phase 2, andpositive current will flow through leakage inductor of phase 2, causingextra power losses. In order to reduce losses due to the body diodeconduction, the controller 102 turns on the low side switch LS2 when HS1is turned on. If the coupling is weak, however, turning on the low sideswitch LS2 when HS1 is turned on can generate negative current flowthough the body diode of the low side switch LS2.

In contrast, in FIG. 6, the controller 104 turns on the low side switchLS2 of phase 2 when the high side switch HS1 of phase 1 is turned ononly if the coupling is strong. The controller 104 does not turn on thelow side switch LS2 of phase 2 when the high side switch HS1 of phase 1is turned on if the coupling is weak. Turning the low side switch LS2 onand off when the coupling strength of the coupled inductor is strong andweak, respectively, eliminates any current flow through the body diodeof the low side switch LS2 in DCM at light load.

In low duty cycle applications, over the entire Vin/Vout operating rangeof the DC-DC converter, the coupling between the phases is strongenough; and in Skip mode, the low side switch LS2 of phase 2 is alwaysturned on when the high side switch HS1 of phase 1 is turned on.Accordingly, if the coupling between the phases is strong, thecontroller 104 turns on the low side switch LS2 of phase 2 when the highside switch HS1 of phase 1 is turned on.

In handheld power applications, however, in the Vin/Vout range, thecoupling between the phases can be strong or weak. If the coupling isstrong, the controller 104 turns on the low side switch LS2 of phase 2when the high side switch HS1 of phase 1 is turned on. If the couplingis weak, the controller 104 does not turn on the low side switch LS2 ofphase 2 when the high side switch HS1 of phase 1 is turned on.

Another method for bypassing the body diode includes using coupledinductors only in CCM. As soon as the converter enters DCM, thecontroller disables all phases with coupled inductor. Only phases withun-coupled inductor are used for DCM. The controller many enable ordisable the un-coupled phases in CCM mode.

FIG. 8 shows an example of a DC-DC converter 200 and a controller 202where the body diode conduction in DCM is prevented (as shown in FIG. 9)using different blocking techniques. Using these blocking techniques,even when the voltage across the low side switch LS2 of the converter200 is greater than the body diode forward voltage, the body diode ofthe low side switch LS2 will not turn on. As explained below in detailwith reference to FIGS. 10-16, the body diode conduction in a low sideswitch can be prevented in DCM using the following techniques, whichincrease the body diode conducting threshold for the low side switch:using a low side switch comprising back-to-back series connectedswitches, switching bulk connections of the low side switch, using a lowside switch comprising a plurality of series-connected switches, orbiasing the bulk of the low side switch to a more negative voltage (ifNMOS switches are used, or more positive voltage if PMOS switches areused).

Using these techniques, when the coupling is strong, the switching nodevoltage LX2 of phase 2 can be negative, and the diode forward voltagecan be below ground (GND). When the coupling is weak, the body diode isautomatically prevented from conducting as follows. Accordingly, nocontrol logic or circuits are needed to determine whether coupling isweak or strong.

FIG. 10 shows an example of a DC-DC converter 200-1 and a controller202-1 where the body diode conduction is prevented in DCM using a lowside switch comprising back-to-back series connected switches. Forexample, in each phase, the low side switch comprises first and secondback-to-back series connected switches, where the first switch isconnected to the switching node (LX1 or LX2) and to the second switch,and the second switch is connected to the first switch and ground asshown. The controller 202-1 generates the control signals HS1, LS1 b,LS1, HS2, LS2 b, and LS2 that drive the switches in phases 1 and 2 asshown in FIG. 11.

Each phase includes a level shifter and driver, and a low voltageselector that are connected to the first switch of the low side switchof each phase as shown. The operation of these components is describedbelow (and shown in FIG. 11) using phase 2 as an example. Similarexplanation obtains for phase 1 when phase 2 is on and phase 1 is off.Other components or logic with similar functionality may be used insteadof these components to prevent body diode conduction as described below.

In phase 2, the level shifter and driver drives the first switch of thelow side switch by converting a signal LS2 b (from the controller 202-1)from a VDD-GND supply rail to a VDD-PL2 supply rail. PL2 is equal to thelower of the switching node voltage LX2 or GND. The low voltage selectorautomatically connects PL2 output by the level shifter and driver to thelower of the switching node voltage LX2 or GND as shown. The secondswitch of the low side switch is driven by the signal LS2 from thecontroller 202-1 as shown in FIG. 11.

In CCM and non-Skip DCM operation, the signal LS2 b is always high (thelow side cascade switch is kept on). In light load Skip mode operation,where inductor current of each phase is not overlapped (e.g., in FIG.11, HS2 turns on after LS1 turns off at IL1 zero crossing), LS2 b is lowonly when HS1 is high. Accordingly, unlike FIG. 6, no control logic orcircuits are needed to determine whether coupling is weak or strong, andbody diode conduction is prevented regardless of coupling strength.

FIG. 12 shows an example of a DC-DC converter 200-2 and a controller202-2 where the body diode conduction is prevented in DCM by switchingbulk connections of the low side switches. The structural arrangementfor switching bulk connections of the low side switches is the same ineach phase; therefore, the structural arrangement for switching bulkconnections of the low side switch of only phase 2 is described.

In phase 2, the low side switch LS2 comprises a first switch S2 aconnected to the drain (and the switching node LX2) and to the bulk ofthe low side switch; and a second switch S2 b connected to the bulk andto the source of the low side switch (i.e., to ground) as shown. Thecontroller 202-2 generates the control signals HS1, LS1, BS1 a, BS1 b,HS2, LS2, BS2 a, and BS2 b that drive the switches in phases 1 and 2 asshown in FIG. 13.

In addition to the switches for switching bulk connections of the lowside switches, each phase includes a level shifter and driver, and a lowvoltage selector that are connected to the low side switch of each phaseas shown. The operation of these components is described below (andshown in FIG. 13) using phase 2 as an example. Similar explanationobtains for phase 1 when phase 2 is on and phase 1 is off. Othercomponents or logic with similar functionality may be used instead ofthese components to prevent body diode conduction as described below.

In phase 2, the level shifter and driver drives the low side switch byconverting a signal LS2 (from the controller 202-2) from a VDD-GNDsupply rail to a VDD-PL2 supply rail. PL2 is equal to the lower of theswitching node voltage LX2 or GND. The low voltage selectorautomatically connects PL2 output by the level shifter and driver to thelower of the switching node voltage LX2 or GND as shown. The controller202-2 generates bulk switching control signals BS2 a and BS2 b tooperate the switches S2 a and S2 b as shown in FIG. 13.

In CCM and non-Skip DCM operation, BS2 a is low, BS2 b is high, S2 a isoff, and S2 b conducts (bulk and source are shorted together). In Skipmode operation, when HS1 is high, states of BS2 a and BS2 b aredetermined by the voltage level at the switching node LX2. If LX2>=0,BS2 a is low, BS2 b is high, and S2 b conducts, shorting bulk and sourcetogether. If LX2<0, BS2 a is high, BS2 b is low, and S2 a conducts,shorting bulk and drain together. Accordingly, unlike FIG. 6, no controllogic or circuits are needed to determine whether coupling is weak orstrong, and body diode conduction is prevented regardless of couplingstrength.

FIG. 14 shows an example of a DC-DC converter 200-3 and a controller202-3 where the body diode conduction is prevented in DCM using a lowside switch comprising a plurality of series-connected switches. Forexample, the low side switch in each phase comprises at least first andsecond series connected switches, where the first switch is connected tothe switching node (LX1 or LX2) and to the second switch, and the secondswitch is connected to the first switch and ground as shown. Thecontroller 202-3 generates the control signals HS1, LS1, HS2, and LS2that drive the switches in phases 1 and 2.

In each phase, a first level shifter and driver is connected to thefirst switch of the low side switch; a second level shifter and driveris connected to the second switch of the low side switch; and so on asshown. The inputs of the first level shifter and driver, the secondlevel shifter and driver, and so on are tied together and are driven bythe switching signal LS1 or LS2 from the controller 202-3 as shown.

Using a plurality of series-connected switches in the low side switchincreases the threshold voltage for body diode conduction in the lowside switch and prevents body diode conduction in the low side switch.For example, the switching node voltage LX2 can be negative N timesforward voltage drop of a body diode of a series connected switch in alow side switch, where N is an integer greater than 1 and denotes thenumber of series-connected switches in the low side switch. Accordingly,unlike FIG. 6, no control logic or circuits are needed to determinewhether coupling is weak or strong, and body diode conduction isprevented regardless of coupling strength.

FIG. 15 shows an example of a DC-DC converter 200-4 and a controller202-4 where the body diode conduction is prevented in DCM by biasing thebulk of the low side switches to a more negative voltage (if NMOSswitches are used, or a more positive voltage if PMOS switches areused). The structural arrangement for biasing the bulk of the low sideswitches is the same in each phase; therefore, the structuralarrangement for biasing the bulk of the low side switch of only phase 2is described.

In phase 2, the low side switch LS2 comprises a first switch S2 aconnected to the bulk and to the source of the low side switch (i.e., toground) as shown; and a second switch S2 b connected to the bulk of thelow side switch and a negative voltage supply (if NMOS switches areused; or a positive voltage supply if PMOS switches are used). Thecontroller 202-4 generates the control signals HS1, LS1, BS1 a, BS1 b,HS2, LS2, BS2 a, and BS2 b that drive the switches in phases 1 and 2 asshown in FIG. 16.

In addition to the switches for biasing the bulk of the low sideswitches, each phase includes a level shifter and driver, and a lowvoltage selector that are connected to the low side switch of each phaseas shown. The operation of these components is described below (andshown in FIG. 16) using phase 2 as an example. Similar explanationobtains for phase 1 when phase 2 is on and phase 1 is off. Othercomponents or logic with similar functionality may be used instead ofthese components to prevent body diode conduction as described below.

In phase 2, the level shifter and driver drives the low side switch byconverting a signal LS2 (from the controller 202-4) from a VDD-GNDsupply rail to a VDD-PL2 supply rail. PL2 is equal to the lower of theswitching node voltage LX2 or GND. The low voltage selectorautomatically connects PL2 output by the level shifter and driver to thelower of the switching node voltage LX2 or GND as shown. The controller202-4 generates control signals BS2 a and BS2 b to operate the switchesS2 a and S2 b as shown in FIG. 16.

When NMOS switches are used, Vneg is a negative voltage generated by theDC-DC converter 200-4 that is more negative than the lowest voltage atthe switching node LX2 can be. Thus, when the bulk of the low sideswitch is connected to Vneg through S2 b, both body diodes of the lowside switch cannot conduct.

In CCM and non-Skip DCM operation, BS2 a is high, BS2 b is low, S2 a ison, and S2 b is off (i.e., bulk and source of the low side switch areshorted together). In Skip mode operation, when HS1 is high, BS2 a islow, BS2 b is high, S2 a is off, and S2 b is on (i.e., bulk of the lowside switch is connected to the negative bias voltage Vneg).Accordingly, unlike FIG. 6, no control logic or circuits are needed todetermine whether coupling is weak or strong, and body diode conductionis prevented regardless of coupling strength.

Another method of preventing negative voltage (if NMOS switches areused, or positive voltage if PMOS switches are used) at the switchingnodes to prevent body diode conduction involves adjusting couplingbetween phases. The coupling inductor can be designed to have moremutual coupling between active phases in DCM. The coupling inductor canbe designed to reduce the coupling voltage across the body diode of thelow side switch to less than the forward voltage drop of the body diodeto prevent body diode conduction.

FIGS. 17 and 18 show an example of a DC-DC converter 300 and acontroller 302 where the body diode conduction is prevented in DCM usingmodified coupled inductor topologies and/or connections. Examples ofmodified coupled inductor topologies and/or connections are shown anddescribed referring to FIGS. 19 and 20 below. The modified coupledinductor topologies and/or connections are used to prevent voltageacross a turned off low side switch from being greater than a forwardvoltage drop of the body diode of the turned off low side switch.

FIGS. 19 and 20 show examples of the modified coupled inductortopologies and/or connections. These modified coupled inductortopologies and/or connections can prevent body diode conduction in DCM.The modified coupled inductor topologies and/or connections can providedifferent types of couplings. For example, the different types ofcouplings can include selective coupling of phases, adjustment ofcoupling factor (weak/strong), multiphase coupling (coupling two or morephases), and asymmetric coupling of phases. The modified coupledinductor topologies and/or connections and the different types ofcouplings are described below.

In designing a coupled inductor, more coupling phase(s) can be added tocertain phase(s); or magnetizing inductance and leakage inductance canbe changed for certain phase(s); and these phase(s) can be used onlyduring Skip mode. The switching node voltage of these specificallydesigned phase(s) will not go negative below (for NMOS switches, orpositive above for PMOS switches) forward voltage drop of a low sideswitch body diode, and the low side switch body diode will not conduct.

In some implementations, coupled inductors (or coupled inductor togetherwith an uncoupled inductor) can be used in CCM while the uncoupledinductor can be used in DCM only. Phase shedding may be implemented forphases with coupled inductor. For example, these operations, includingselecting coupled inductors (or coupled inductor together with anuncoupled inductor) in CCM, selecting an uncoupled inductor in DCM only,and phase shedding, can be performed by the controller 302 shown in FIG.18.

In an N phase converter (where N>3), coupled inductors can be designedto have asymmetrical coupling structure. For example, in a neighborcoupling case, each phase is coupled to neighboring two phases. Toprevent body diode conduction at light load, phase A may be designed tocouple to all other phases, and only phase A is used during light loadoperation. With more mutual coupling between phase A and other phases,when the high side switch of phase A turns on, the voltage across thelow side switches of other phases can be greatly reduced to preventconduction of the low side switch body diode.

The coupled inductor can be designed with specific magnetizinginductance (L_(m)) and leakage inductance (L_(k)) values. Themagnetizing inductance (L_(m)) and leakage inductance (L_(k)) values canbe selected for designated Vin/Vout operation range of the converter toensure that the coupling voltage across the body diode of the low sideswitch is not high enough to conduct the body diode.

The inductances can be expressed in the form of a matrix (using linearalgebra) called an inductance matrix that captures the details of everywinding coupling relative to every other winding, and is a more generalcase that applies when there are more than two windings or when thecoupling is not identical between phases. Magnetizing and leakageinductances are typically used to describe coupled inductors fortwo-phase applications. To fully describe an N-phase coupled inductorstructure, an inductance matrix is commonly used. For N=2, the matrix isequivalent to the magnetizing and leakage inductance form.

One example of an inductance matrix is shown below.

L-Matrix Definition (defined in terms of a buck converter topology tofacilitate subsequent discussion):

$\begin{bmatrix}{V_{{LX}\; 1} - V_{OUT}} \\{V_{{LX}\; 2} - V_{OUT}} \\\vdots \\{V_{LXN} - V_{OUT}}\end{bmatrix} = {\begin{bmatrix}L_{11} & L_{12} & \ldots & L_{1N} \\L_{21} & L_{22} & \ldots & L_{2N} \\\vdots & \vdots & \ddots & \vdots \\L_{N\; 1} & L_{N\; 2} & \ldots & L_{NN}\end{bmatrix}\begin{bmatrix}\frac{{dI}_{1}}{dt} \\\frac{{dI}_{2}}{dt} \\\vdots \\\frac{{dI}_{N}}{dt}\end{bmatrix}}$

This is related to magnetizing (L_(M)) and leakage (L_(K)) for N=2 asfollows:

L₁₁ = L₂₂ = L_(M) + L_(K) L₂₁ = L₁₂ = −L_(M)$L_{Matrix} = {\begin{bmatrix}L_{11} & L_{12} \\L_{21} & L_{22}\end{bmatrix} = \begin{bmatrix}{L_{M} + L_{K}} & {- L_{M}} \\{- L_{M}} & {L_{M} + L_{K}}\end{bmatrix}}$

For N=2, the following procedure can ensure that the voltage that iscoupled across the body diode is less than a forward voltage drop of thebody diode:

First, solve this system of equations for V_(LX2)

$\begin{bmatrix}{V_{IN} - V_{OUT}} \\{V_{{LX}\; 2} - V_{OUT}}\end{bmatrix} = {\begin{bmatrix}L_{11} & L_{12} \\L_{21} & L_{22}\end{bmatrix}\begin{bmatrix}\frac{{dI}_{1}}{dt} \\0\end{bmatrix}}$$V_{{LX}\; 2} = {{{\frac{L_{2}}{L_{11}}V_{IN}} + {\left( {1 = \frac{L_{21}}{L_{11}}} \right)V_{OUT}}} = {{{- \frac{L_{M}}{L_{M} + L_{K}}}V_{IN}} + {\frac{{2L_{M}} + L_{K}}{L_{M} + L_{K}}V_{OUT}}}}$

Second, choose L_(M) and L_(K) such that V_(LX2) does not turn on thebody diode:

V _(LX2) >−|V _(diode)|

For generalized N-phase, the same procedure is followed. First, solvethe system of equations for V_(LX,i), where i is in the set of phasesthat is not driven by the high- or low-side switches. For example,assume phase 1 is driven and phases 2-N are not.

$\begin{bmatrix}{V_{IN} - V_{OUT}} \\{V_{{LX}\; 2} - V_{OUT}} \\\vdots \\{V_{LXN} - V_{OUT}}\end{bmatrix} = {\begin{bmatrix}L_{11} & L_{12} & \ldots & L_{1\; N} \\L_{21} & L_{22} & \ldots & L_{2\; N} \\\vdots & \vdots & \ddots & \vdots \\L_{N\; 1} & L_{N\; 2} & \ldots & L_{NN}\end{bmatrix}\begin{bmatrix}\frac{{dI}_{1}}{dt} \\0 \\\vdots \\0\end{bmatrix}}$

Second, choose L_(ik), where i=[1 to N] and k=[1 to N] such thatV_(LX,i), for i=[2 to N] is not less than the body diode voltage. Thisprocedure can be followed for any combination of phases driven. Thenumber of phases driven does not need to be 1.

In an N phase converter (N>2), the coupled inductor can be designed tohave more phases coupling together, such as neighbor coupling (eachphase coupling to neighboring two phases) or mutual coupling (each phasecoupling to all other phases), which can reduce the coupling voltageacross the low side switch and prevent the body diode of the low sideswitch from conducting. In addition, adding more phases in the converterand coupling the phases together can further decrease the couplingvoltage across the low side switch and prevent the body diode of the lowside switch from conducting at light load.

FIG. 21 shows a method 400 for preventing conduction of a body diode ofa low side switch of a coupled-inductor DC-DC converter operating atlight load in DCM by detecting strong or weak coupling. At 402, controldetermines if the converter is operating in DCM. At 404, if theconverter is operating in DCM, control detects whether the couplingbetween inductors of the coupled inductor is strong or weak. At 408, ifthe coupling is strong, if high side switch of a first phase is on andlow side switch of a second phase is off, turn on low side switch of thesecond phase; if low side switch of the second phase is on, keep it on.At 410, if the coupling is weak, if high side switch of a first phase ison and low side switch of a second phase is off, do not turn on low sideswitch of a second phase; If high side switch of a first phase is on andlow side switch of a second phase is on, keep low side switch of thesecond phase on.

FIG. 22 shows a method 450 for preventing conduction of a body diode ofa low side switch of a coupled-inductor DC-DC converter operating atlight load in DCM by using a low side switch comprising back-to-backseries connected switches. At 452, a low side switch in each phase ofthe converter comprises back-to-back series connected first and secondswitches. At 454, the first switch is connected to a switching node ofthe phase, and the second switch is connected to ground. At 456, controldrives the first switch using a first signal and the second switch usinga second signal.

At 458, control converters the first signal from a power supply level ofthe converter to a lower power level (e.g., from a VDD-GND supply railto a VDD-PL2 supply rail, where PL2 is equal to the lower of theswitching node voltage or GND). Further, control automatically connectslevel shifter output (PL2) to the switching node voltage or GNDwhichever is lower. At 460, in CCM and non-skip DCM operation, controlholds the first signal always high. At 462, in light load skip modeoperation, to prevent the low side switch body diode from conducting,control holds the first signal low only when a high side switch of acoupled phase is on.

FIG. 23 shows a method 500 for preventing conduction of a body diode ofa low side switch of a coupled-inductor DC-DC converter operating atlight load in DCM by switching bulk connections of the low side switch.At 502, in each phase, a first switch is connected across drain and bulkof a low side switch, and a second switch is connected across bulk andsource of the low side switch. At 504, control drives the first switchusing a first signal and the second switch using a second signal.

At 506, control converts a low side switching signal (e.g., LS2) from apower supply level of the converter to a lower power level (e.g., from aVDD-GND supply rail to a VDD-PL2 supply rail, where PL2 is equal to thelower of the switching node voltage or GND). Further, controlautomatically connects level shifter output (PL2) to the switching nodevoltage or GND whichever is lower.

At 508, in CCM and non-skip DCM operation, control turns the firstswitch off and the second switch on to short the bulk and source of thelow side switch. At 510, in light load skip mode operation, when a highside switch of a first phase is on, to prevent the low side switch bodydiode of a second phase from conducting, control operates the first andsecond switches associated with the low side switch of the second phasedepending on the switching node voltage as follows: control turns thefirst switch off and the second switch on to short the bulk and sourceof the low side switch in the second phase if the switching node voltagein the second phase is greater than or equal to 0; and control turns thefirst switch on and the second switch off to short the bulk and drain ofthe low side switch in the second phase if the switching node voltage inthe second phase is less than 0.

FIG. 24 shows a method 550 for preventing a body diode of a low sideswitch from conducting at light load in a converter using a coupledinductor in DCM by using a low side switch comprising a plurality ofseries-connected switches. At 552, in each phase, a plurality of seriesconnected switches (e.g., a first switch connected in series with asecond switch) is arranged as a low side switch. At 554, control drivesthe plurality of series connected switches (e.g., the first switch andthe second switch) using a LS switching signal. At 556, the switchingnode voltage in each phase can be negative N times the forward voltagedrop of a body diode of a series connected switch in a low side switch,which increases the threshold voltage for body diode conduction in thelow side switch and prevents body diode conduction in the low sideswitch.

FIG. 25 shows a method 600 for preventing conduction of a body diode ofa low side switch of a coupled-inductor DC-DC converter operating atlight load in DCM by biasing the bulk of the low side switch to a morenegative voltage (if NMOS switches are used, or a more positive voltageif PMOS switches are used). At 602, in each phase of the converter, afirst switch is connected across bulk and source of the low side switch,and a second switch is connected across the bulk of the low side switchand a voltage source. The voltage source supplies negative or positivevoltage depending on whether the switches of the converter are NMOS andPMOS.

At 604, control drives the first switch using a first signal and thesecond switch using a second signal. At 606, control converts a low sideswitching signal (e.g., LS2) from a power supply level of the converterto a lower power level (e.g., from a VDD-GND supply rail to a VDD-PL2supply rail, where PL2 is equal to the lower of the switching nodevoltage or GND). Further, control automatically connects level shifteroutput (PL2) to the switching node voltage or GND whichever is lower.

At 608, in CCM and non-skip DCM operation, control turns the firstswitch on and the second switch off to short the bulk and source of thelow side switch. At 610, in light load skip mode operation, when a highside switch of a first phase is on, to prevent the low side switch bodydiode in the second phase from conducting, control turns the firstswitch off and the second switch on to connect the bulk of the low sideswitch to the voltage source in the second phase.

The teachings of the present disclosure described with reference tolow-side switch body diodes can also be applied to high-side switch bodydiodes. Further, while in some applications, the converters describedmay operate in a voltage range where the high-side body diode neverconducts, there are other applications where the high-side body diodewould conduct. The teachings of the present disclosure are also equallyapplicable to multi-level converters having more than 2 switches perphase.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” or the term “controller” may refer to, be part of, orinclude: an Application Specific Integrated Circuit (ASIC); a digital,analog, or mixed analog/digital discrete circuit; a digital, analog, ormixed analog/digital integrated circuit; a combinational logic circuit;a field programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks,flowchart components, and other elements described above serve assoftware specifications, which can be translated into the computerprograms by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A multiphase DC-DC converter comprising: acoupled inductor that includes a plurality of inductors, each inductorbeing coupled to two neighboring inductors or to rest of the inductors;N phases of the multiphase DC-DC converter respectively connected to theplurality of inductors, where N is an integer greater than 2; and acontroller that operates the multiphase DC-DC converter in continuousconduction mode and in discontinuous conduction mode, wherein bodydiodes of switches in the N phases do not conduct when the multiphaseDC-DC converter operates in discontinuous conduction mode.
 2. Amultiphase DC-DC converter comprising: a coupled inductor that includesfirst and second inductors coupled together; a first phase includingfirst high side and low side switches connected to the first inductor; asecond phase including second high side and low side switches connectedto the second inductor; a third switch connected across bulk and sourceterminals of the second low side switch; a fourth switch connectedacross bulk terminal of the second low side switch and a voltage source;and a controller that: drives the first and second high side switchesand the first and second low side switches to operate the multiphaseDC-DC converter in discontinuous conduction mode; and turns off thethird switch and turns on the fourth switch in response to the firsthigh side switch being turned on, wherein a body diode of the second lowside switch does not conduct.
 3. The multiphase DC-DC converter of claim2 wherein the voltage source supplies a voltage of the same polarity asthe type of a dopant used for the switches.
 4. The multiphase DC-DCconverter of claim 2 wherein in each of the first and second phases, inresponse to the switches using N type dopant, the voltage sourcesupplies a negative voltage that is more negative than a lowest voltageat a switching node to prevent body diodes of the first and second lowside switches from conducting.
 5. The multiphase DC-DC converter ofclaim 2 wherein each of the first and second phases includes a levelshifter that converts a first control signal from the controller from afirst supply rail to a second supply rail comprising a voltage lowerthan a switching node voltage and that outputs a second control signalto drive the first or second low side switch, wherein body diodes of thefirst and second low side switches do not conduct irrespective ofstrength of coupling between the first inductor and the second inductor.6. The multiphase DC-DC converter of claim 2 wherein in response to thecontroller operating the multiphase DC-DC converter in continuousconduction mode, the controller turns on the third switch and turns offthe fourth switch.
 7. The multiphase DC-DC converter of claim 2 whereinin response to the controller operating the multiphase DC-DC converterin skip mode where the second low side switch is turned on when thefirst high side switch is turned on, the controller turns off the thirdswitch and turns on the fourth switch.
 8. A multiphase DC-DC convertercomprising: a coupled inductor that includes first and second inductorscoupled together; a third inductor that is not coupled to the first andsecond inductors; first and second phases of the multiphase DC-DCconverter respectively connected to the first and second inductors; athird phase of the multiphase DC-DC converter connected to the thirdinductor; and a controller that selects the first and second phases inresponse to operating the multiphase DC-DC converter in continuousconduction mode, and selects the third phase in response to operatingthe multiphase DC-DC converter in discontinuous conduction mode.